The present invention relates generally to automatic, responsive, computer-controlled systems for delivering pulsed medications to patients.
The basic idea of a closed-loop system for dispensing medication exists in biomedical systems. One such device, the Cardiff machine, implements a closed-loop system for dispensing oxytocin via continuous infusion. Oxytocin is a hormone used by physicians for controlling the process of labor stimulation and augmentation. Use of the Cardiff machine involves starting infusion at a low rate and progressively doubling that rate about every 15 minutes until a rate of 32 milliunits of oxytocin per minute is reached. Using a feedback mechanism, the infusion is suspended for 2.5 minutes after the onset of each contraction. If the contractions begin occurring at intervals of 2.5 minutes or less, the dose rate becomes constant.
Problems exist with that method of feedback control. First, because of the delay in the effect of oxytocin, the eventual rate produced is often too high. Second, since oxytocin stimulates the production of natural hormones having effects similar to those produced by oxytocin, varying or reducing the oxytocin infusion rates during labor may become necessary. Needs exist for medication delivery systems that have expedited responses to existing and developing medical conditions.
Efforts to improve the operational capabilities of closed-loop systems have proven unsuccessful. In one modified closed-loop system, the infusion rate is based on the average mark-space ratio exhibited by contractions, where a mark is considered to be occurring while the intrauterine pressure exceeds a certain value and a space is considered to be occurring otherwise. That feedback mechanism approach is ineffective because it makes no distinction between contractions of different strengths. Thus, that feedback mechanism treats the following in an identical way if the same mark-space ratio exists: (a) frequent, very strong contractions (e.g., ones whose peaks reach 75 mg Hg); (b) frequent contractions of moderate strengths (e.g., ones whose peaks reach 45 mg Hg); (c) frequent, very weak contractions (e.g., ones whose peaks do not reach 30 mg Hg). While case (b) may constitute satisfactory labor, case (a) may represent a case of hypertonus with danger of fetal distress which demands oxytocin administration to be reduced or suspended. Alternatively, case (c) may represent a condition in which the labor is not being significantly advanced, thus reducing fetal oxygen without receiving the benefits of accelerated labor. Needs exist for medication delivery systems that provide better and more accelerated mechanisms of feedback control.
Systems for providing medications of oxytocin in doses released in discrete intervals, rather than in a continuous manner, have proven inadequate. One system uses two fixed, but operator settable, time intervals, T1 and T2. T1 is the time period between doses of oxytocin and T2 is the duration of each dose. In that system, the pumping means is disabled in response to a contraction, the count for T1 is reset to zero in response to a contraction, and the size of the measured doses, as defined by time interval T2, is not altered by the system. In particular, T2 is not altered in response to the strength or frequency of contractions. Those results are too stringent and are undesirable. Needs exist for biomedical systems that administer dosed medications of oxytocin with size and frequency responsive to feedback signals.
Existing fetal monitoring systems use displays that show intrauterine pressure. Those displays are intended for the medical staff, and generally do not attract the interest or attention of the patient in labor. Needs exist for oxytocin delivery systems that have displays which are patient friendly and therapeutically relaxing.